Pressure-sensitive adhesives are widely used in the industry. A pressure-sensitive adhesive (PSA) is an adhesive that bonds with an adherent when pressure is applied to it. This contrasts, for example, with adhesives that are activated by heat, irradiation or a chemical reaction.
Pressure-sensitive adhesives can be applied to a support material as an emulsion or dispersion, which is then dried to remove the liquid carrier, or, alternatively, as a solid that is applied in heated form to reduce its viscosity.
Typical PSA compositions for paper labels are water-based dispersions that primarily contain an elastomer and a tackifier. Usually, the elastomer used in these formulations is an acrylate polymer and the tackifier is based on rosin ester. The high molecular weight acrylate polymer provides the formulation with elasticity, cohesion and resistance to shear, while the viscous, low molecular weight tackifier makes the formulation more adhesive.
There remains a need for improved PSA compositions with better adhesion to difficult substrates, like polyethylene, polypropylene and cardboard, and better cohesion and resistance to shear. The present invention addresses this need.